U.S. patent application number 12/269556 was filed with the patent office on 2009-03-12 for ink jet printing apparatus, ink jet printing method, and preliminary discharge control method.
This patent application is currently assigned to c/o Canon Kabushiki Kaisha. Invention is credited to Tetsuya EDAMURA, Akiko MARU, Yoshiaki MURAYAMA, Kiichiro TAKAHASHI, Minoru TESHIGAWARA.
Application Number | 20090066736 12/269556 |
Document ID | / |
Family ID | 37617952 |
Filed Date | 2009-03-12 |
United States Patent
Application |
20090066736 |
Kind Code |
A1 |
EDAMURA; Tetsuya ; et
al. |
March 12, 2009 |
INK JET PRINTING APPARATUS, INK JET PRINTING METHOD, AND
PRELIMINARY DISCHARGE CONTROL METHOD
Abstract
On performing a predetermined printing operation, whether or
not, among a plurality of printing elements, only a part of the
printing elements are applied is detected. If it is judged that
only the part of the printing elements are used, a judgment is made
whether or not the preliminary discharge operation is performed
based on the number of discharges for the part of the printing
elements, and if it is not judged that only the part of the
printing elements are used, a judgment is made whether or not the
preliminary discharge operation is performed based on the number of
discharges for all of the printing elements of the printing head.
This eliminates an unnecessary preliminary discharge for
non-printing elements even in a printing operation mode in which
only a part of the printing elements are applied.
Inventors: |
EDAMURA; Tetsuya;
(Kawasaki-shi, JP) ; TAKAHASHI; Kiichiro;
(Yokohama-shi, JP) ; TESHIGAWARA; Minoru;
(Yokohama-shi, JP) ; MARU; Akiko; (Kawasaki-shi,
JP) ; MURAYAMA; Yoshiaki; (Tokyo, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
c/o Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
37617952 |
Appl. No.: |
12/269556 |
Filed: |
November 12, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11477459 |
Jun 30, 2006 |
7465006 |
|
|
12269556 |
|
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Current U.S.
Class: |
347/9 |
Current CPC
Class: |
B41J 2/16517 20130101;
B41J 11/06 20130101; B41J 2/1753 20130101; B41J 2/17553 20130101;
B41J 2/17546 20130101 |
Class at
Publication: |
347/9 |
International
Class: |
B41J 29/38 20060101
B41J029/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 7, 2005 |
JP |
2005-198953 |
Claims
1. An ink jet printing apparatus for printing an image on a
printing medium using a printing head having a plurality of
printing elements to discharge ink, comprising: means for counting
the number of discharges by the printing elements of the printing
head; means for judging whether or not a preliminary discharge
operation of the printing head is necessary, based on the number of
discharges obtained by the counting means; and means for performing
the preliminary discharge by the printing elements of the printing
head in accordance with a result of the judgment by the judging
means, wherein when a printing operation is performed using only a
part of the printing elements among the plurality of the printing
elements of the printing head, the judging means judges whether or
not the preliminary discharge operation is necessary based on the
number of discharges counted for the part of the printing
elements.
2.-9. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an ink jet printing
apparatus and a method of controlling preliminary discharge of the
apparatus.
[0003] 2. Description of the Related Art
[0004] An ink jet printing head discharges an ink droplet within a
nozzle from a minute hole (hereinafter referred to as a discharge
port) of the nozzle toward a printing medium to perform printing.
As the printing head discharges the ink, the ink within the nozzle
is decreased and a new ink is charged from an ink chamber by
capillary force.
[0005] However, when the ink is not discharged over a long period
of time, evaporation of moisture and a solvent of the ink may cause
a color material to be precipitated at the discharge port and the
precipitated color material may form a film at the discharge port,
thus preventing a normal ink discharge. A kinetic energy produced
to discharge the ink droplet by a printing operation of the
printing head is consumed in breaking the film. As a result, the
ink droplet cannot achieve a sufficient discharge speed and thus
cannot be printed in a desired position on the printing medium.
[0006] To cope with this, the ink jet printing apparatus performs a
preliminary discharge operation to move the printing head outside
the printing medium and to discharge the ink at a predetermined
location before a complete film is not formed at the discharge
port. By performing the preliminary discharge operation, the nozzle
can be maintained in a condition to do a normal ink discharge
during printing.
[0007] In general, a serial-scanning ink jet printing apparatus
judges whether or not a predetermined time has passed since a
previous preliminary discharge at the time of an inversion during
reciprocating scanning of a carriage with a printing head, and
performs such control as to move the printing head outside a
printing medium for a preliminary discharge if the predetermined
time has passed.
[0008] However, frequent preliminary discharge operations cause
printing speed to be decreased, and also involve the disadvantage
that consumption of the ink except in actual printing leads to a
rise in running costs.
[0009] In order to eliminate such disadvantage, for example,
Japanese Patent Application Laid-open No. 63-252748 discloses a
control method, wherein the number of actuations of a plurality of
nozzles is measured in a predetermined time, and if the value
measured is less than a predetermined number, a preliminary
discharge is performed, while if the value measured is equal to or
greater than the predetermined number, the preliminary discharge is
not performed. This method eliminates the preliminary discharge
operation of nozzles undergoing frequent discharge operations, and
therefore the time and amount of ink wasted in the preliminary
discharge are reduced.
[0010] Also, Japanese Patent Application Laid-open No. 2004-082629
discloses a method, wherein the number of actuations of a plurality
of nozzles is measured in a predetermined time, a judgment is made
whether the value measured is equal to or greater than a
predetermined number, and based on the judgment, a subsequent
printable time is adjusted. And with each completion of a printing
scanning, the adjusted printable time is compared with the time
required for subsequent printing scanning, and a preliminary
discharge operation is performed if the printable time is shorter.
A control method like this does not perform the preliminary
discharge carelessly with each printing scanning even when the time
required for one printing scanning is equivalent to
discharge-guarantee time of non-discharge nozzles. This enables the
preliminary discharge to be efficiently performed without reducing
throughput as much as possible.
[0011] The preliminary discharge of the ink jet printing apparatus
is an important operation required to maintain image quality. On
the other hand, however, the preliminary discharge can trigger an
increased ink consumption and decreased throughput. Based on this
standpoint, one of the problems in recent ink jet printing
apparatuses is how efficiently and unwastedly the preliminary
discharge operation is performed.
[0012] In recent years, there has been an increasing demand for
so-called "margin-less printing" in which an image is formed on a
printing medium without setting in any margin. And a number of
arrangements or printing methods which enable such printing have
already been proposed (refer to Japanese Patent Application
Laid-open No. 2003-127353 and No. 2004-1416). When, in the
"margin-less printing", printing is performed in the vicinity of an
endmost portion of the printing medium, support of the printing
medium becomes unstable, which may cause conveyance accuracy of the
printing medium to be decreased. Also, there are concerns that ink
discharged running off the printing medium may contaminate an
inside of the apparatus or of a non-printed area of the printing
medium. Therefore, as disclosed in the above-mentioned publication,
No. 2004-1416, for printing in the vicinity of the endmost portion
of the printing medium, a method is generally adopted in which the
number of nozzles to be practically applied to the printing is
limited.
[0013] Even when such "margin-less printing" is performed, the
preliminary discharge method described in the above-mentioned
publication, No. 63-252748 or No. 2004-082629 has been
conventionally adopted. However, with a limited number of nozzles
for printing on the endmost portion, non-discharge nozzles which
are not involved in printing always exist, and therefore the
conventional preliminary discharge control methods are not able to
bring about an efficient preliminary discharge operation. That is,
during printing in the vicinity of the endmost portion of the
printing medium, due to the nozzles which are not involved in the
printing, more preliminary discharge operations than required are
performed, and accordingly the ink is improperly consumed,
resulting in a decreased throughput.
SUMMARY OF THE INVENTION
[0014] The present invention has been made in view of the foregoing
problem and therefore has an object to provide an ink jet printing
apparatus and a preliminary discharge control method which are
capable of performing a more efficient preliminary discharge
operation in terms of ink consumption and throughput even when the
number of nozzles to be used is limited for image formation as in
the "margin-less printing".
[0015] The first aspect of the present invention is an ink jet
printing apparatus for printing an image on a printing medium using
a printing head having a plurality of printing elements to
discharge ink, comprising: means for counting the number of
discharges by the printing elements of the printing head; means for
judging whether or not a preliminary discharge operation of the
printing head is necessary, based on the number of discharges
obtained by the counting means; and means for performing the
preliminary discharge by the printing elements of the printing head
in accordance with a result of the judgment by the judging means,
wherein when a printing operation is performed using only a part of
the printing elements among the plurality of the printing elements
of the printing head, the judging means judges whether or not the
preliminary discharge operation is necessary based on the number of
discharges counted for the part of the printing elements.
[0016] The second aspect of the present invention is an ink jet
printing apparatus for printing an image on a printing medium using
a printing head having a plurality of printing elements to
discharge ink, comprising: print control means for performing a
first printing operation in which printing is performed on a
central part of the printing medium using the plurality of the
printing elements and a second printing operation in which printing
is performed on front and rear portions of the printing medium
using a part of the printing elements smaller in number than the
plurality of printing elements; means for counting the number of
discharges by the printing elements of the printing head; means for
judging whether or not a preliminary discharge operation of the
printing head is necessary, based on the number of discharges
obtained by the counting means; and means for performing the
preliminary discharge by the printing elements of the printing head
in accordance with a result of the judgment by the judging means,
wherein the judging means, when the second printing operation is
performed, judges whether or not the preliminary discharge
operation is necessary based on the number of discharges counted
for the part of the printing elements, and when the first printing
operation is performed, judges whether or not the preliminary
discharge operation is necessary based on the number of discharges
counted for the plurality of the printing elements.
[0017] The third aspect of the present invention is an ink jet
printing apparatus for printing an image on a printing medium using
a printing head including a plurality of printing elements to
discharge ink, comprising: means for detecting whether or not only
a part of the printing elements among the plurality of the printing
elements are used for a printing operation; means for counting the
number of discharges by the printing elements for the printing
operation; means for judging whether or not a preliminary discharge
operation of the printing head is necessary based on the number of
s discharges obtained by the counting means; and means for
performing the preliminary discharge by the printing elements of
the printing head in accordance with a result of the judgment by
the judging means, wherein the judging means, if the detecting
means detects that only the part of the printing elements are used,
judges whether or not the preliminary discharge operation is
necessary based on the number of discharges for the part of the
printing elements, and if the detecting means does not detect that
only the part of the printing elements are used, judges whether or
not the preliminary discharge operation is necessary based on the
number of discharges for all of the printing elements of the
printing head.
[0018] The forth aspect of the present invention is an ink jet
printing method for printing an image on a printing medium using a
printing head including a plurality of printing elements to
discharge ink, comprising the steps of: counting the number of
discharges by the printing elements of the printing head; judging
whether or not a preliminary discharge operation of the printing
head is necessary, based on the number of discharges obtained by
the counting step; and performing the preliminary discharge by the
printing elements of the printing head in accordance with a result
of the judgment, wherein, when a printing operation is performed
using only a part of the printing elements among the plurality of
printing elements of the printing head, in the judging step,
whether or not the preliminary discharge operation is necessary is
judged based on the number of discharges counted for the part of
the printing elements.
[0019] The fifth aspect of the present invention is an ink jet
printing method for printing an image on a printing medium using a
printing head having a plurality of printing elements to discharge
ink, comprising: a first printing step of performing printing on a
central part of the printing medium using the plurality of the
printing elements; a second printing step of performing printing on
front and rear portions of the printing medium using a part of the
printing elements smaller in number than the plurality of printing
elements; a counting step of counting the number of discharges by
the printing elements of the printing head; a judging step of
judging whether or not a preliminary discharge operation of the
printing head is necessary, based on the number of discharges
obtained by the counting step; and a step of performing the
preliminary discharge by the printing elements of the printing head
in accordance with a result of the judgment, wherein, for the
second printing step, whether or not the preliminary discharge
operation is necessary is judged based on the number of discharges
counted for the part of the printing elements in the judging step,
and for the first printing step, whether or not the preliminary
discharge operation is necessary is judged based on the number of
discharges counted for the plurality of the printing elements in
the judging step.
[0020] The sixth aspect of the present invention is a preliminary
discharge control method for an ink jet printing apparatus for
printing an image on a printing medium using a printing head having
a plurality of printing elements to discharge ink, comprising the
steps of: detecting whether or not only a part of the printing
elements among the plurality of printing elements are used for a
printing operation; counting the number of discharges from each of
the printing elements for the printing operation; judging whether
or not a preliminary discharge operation of the printing head is
necessary based on the number of discharges obtained by the
counting step; and performing the preliminary discharge by the
printing elements of the printing head in accordance with a result
of the judgment by the judging step, wherein if it is detected that
only the part of the printing elements are used in the detecting
step, whether or not the preliminary discharge operation is
necessary is judged based on the number of the discharges for the
part of the printing elements in the judging step, and if it is not
detected that only the part of the printing elements are used in
the detecting step, whether or not the preliminary discharge
operation is necessary is judged based on the number of discharges
for all of the printing elements of the printing head in the
judging step.
[0021] The above and other objects, effects, features and
advantages of the present invention will become more apparent from
the following description of embodiments thereof taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is an external perspective view showing an outline of
a construction of an ink jet printing apparatus as a typical
embodiment of the present invention;
[0023] FIG. 2 is a detail drawing (a perspective view) of a
printing head cartridge used in the embodiment of the present
invention as viewed from a discharge port side;
[0024] FIG. 3 is a block diagram showing a control configuration of
a printing apparatus applied in the embodiment of the present
invention;
[0025] FIGS. 4A and 4B are enlarged views of a platen provided in
the printing apparatus in the embodiment of the present
invention;
[0026] FIGS. 5A to 5C are schematic views illustrating a positional
relationship between a printing medium and a printing head in the
vicinity of the platen when "margin-less printing" is
performed;
[0027] FIG. 6 is a schematic view illustrating an arrangement of
discharge ports of a printing head applied in the embodiment of the
present invention and an area of discharge ports that practically
perform a discharge operation when printing is performed on front
and rear edges in the "margin-less printing";
[0028] FIG. 7 is a flow chart illustrating a preliminary discharge
control processing; and
[0029] FIG. 8 is a flow chart illustrating an interrupt processing
by an interrupt timer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Preferred embodiments of the present invention will
hereinafter be described in detail with reference to the accompany
drawings. A term "printing" as used herein refers not only to
formation of significant information such as characters and
graphics but also broadly to formation of images, figures,
patterns, and the like on a printing medium, or processing of the
medium, regardless of whether they are significant or insignificant
and whether or not they are embodied so as to be visually perceived
by human beings. Also, a term "printing medium" refers not only to
paper for use in common printing apparatus but also broadly to
ink-acceptable materials such as cloth, a plastic film, a metal
sheet, glass, ceramics, wood, and leather. Further, a term "ink" is
broadly interpreted as in the definition of the "printing"
described above, and refers to a liquid which, when applied to the
printing medium, can form images, figures, patterns, and the like,
can process the printing medium, or can process the ink (for
example, solidify or insolubilize a coloring material in the ink
applied to the printing medium). Furthermore, a term "nozzle"
refers generally to a discharge port to a fluid channel
communicating therewith and an element which produces energy to be
utilized for ink discharge unless otherwise noted.
[0031] Additionally, a term "margin-less printing" as used herein
means doing printing on at least one (one edges) of front and rear
edges of the printing medium without setting in any margin. The
margin-less printing generally requires that the size of a printing
area be greater than that of the printing medium, but it is
acceptable that the size of the printing area corresponds to that
of the printing medium.
<Description of the Ink Jet Printing Apparatus>
[0032] FIG. 1 is an external perspective view showing an outline of
a construction of an ink jet printing apparatus 1 as a typical
embodiment of the present invention. Referring to the figure, there
is shown a carriage 2 capable of moving in the direction of arrow A
shown with a printing head cartridge 3 mounted. The printing head
cartridge 3 is equipped with a printing head to discharge ink in
accordance with an image signal and a removable ink tank 6 to
supply the ink to this printing head. The printing apparatus 1 in
the present embodiment allows for color printing and the printing
head cartridge 3 is equipped with four ink tanks 6 containing
magenta (M), cyan (C), yellow (Y), and black (Bk) inks,
respectively. These four ink tanks 6 are independently removably
attached to the printing head cartridge 3. Each of the color inks
contained in the ink tanks 6 is supplied to the printing head with
a discharge operation.
[0033] FIG. 2 is a detail drawing (a perspective view) of the
printing head cartridge 3 used in the present embodiment as viewed
from a discharge port side. The printing head cartridge 3 is shown
inverted compared with a normal service condition. Discharge port
arrays, 4OBk, 40C, 40M, and 40Y are designed to discharge four
color inks, Bk (black), C (cyan), M (magenta), and Y (yellow),
respectively. The ink tank 6 of each color is configured to be
attached from the direction of an arrow in the figure.
[0034] The printing head in the present embodiment adopts an ink
jet system in which thermal energy is used to discharge the ink and
has an electrothermal converter to produce thermal energy within
each individual nozzle. For printing (discharge), according to
image signals, electrical energy is applied to each individual
electrothermal converter, where it is converted into thermal
energy. Due to rapid heat generation, film boiling takes place in
the ink near the electrothermal converter, and by growth and
contraction of bubbles, a given amount of ink is discharged from
the discharge port.
[0035] The printing head cartridge 3 has a contact surface 43 to
establish and maintain an electrical connection with the carriage
2. Depending on printing signals received from the contact surface
43, the printing head 3 can selectively discharge the ink from a
plurality of nozzles (discharge ports).
[0036] Referring again to FIG. 1, the carriage 2 is coupled to a
part of a drive belt 7 of a transmission mechanism to transmit a
driving force of a carriage motor M1, and is slidably guided and
supported along a guide shaft 13 in the direction of arrow A.
Therefore, the carriage 2 is arranged to be able to reciprocate
along the guide shaft 13 through normal and reverse rotations of
the carriage motor M1.
[0037] Along the moving direction (the direction of arrow A) of the
carriage 2, a scale 8 to indicate an absolute position of the
carriage 2 is provided. The scale 8 in the present embodiment is
made of a transparent PET film on which a black bar is printed at a
predetermined pitch. One end of the scale 8 is fixed to a chassis 9
and the other is supported by a blade spring (not shown).
[0038] With the arrangement described above, while the carriage 2
is doing scanning, the printing head 3 can discharge the ink at an
appropriate timing according to the positional information. This
allows an image corresponding to one printing scanning to be formed
on the printing medium P. In a position opposite to the printing
head 3, a platen (not shown in FIG. 1) is disposed in such a manner
as to support the printing medium P from the underside thereof. The
printing apparatus 1 in the present embodiment is a printing
apparatus capable of "margin-less printing". For that purpose the
platen is made to have a special feature, but the details of the
platen will be described later.
[0039] When one printing scanning is performed, the printing medium
P is conveyed in the direction of arrow B by a conveying mechanism
to be described below. A conveyor motor M2 (not shown in FIG. 1)
functions as a driving force of the conveying mechanism and a
conveying roller 14 makes contact with the printing medium P to
convey it. A driving force of the conveyor motor M2 is transmitted
to the conveying roller 14 through an intermediate gear (not shown)
and a conveying roller gear 17 fixed to one end of the conveying
roller 14. The printing medium P is brought into contact with the
conveying roller 14 by a pinch roller 15 urged by a spring (not
shown) and is conveyed in the direction of arrow B with rotation of
the conveying roller 14. In addition, the pinch roller 15 is
rotatably supported by a pinch roller holder 16.
[0040] A discharging roller 20 discharges the printing medium P on
which an image is formed outside the printing apparatus. The
discharging roller 20 is also rotated by the driving force
transmitted from the conveyor motor M2. The printing medium P is
brought into contact with the discharging roller 20 by a spur
roller urged by a spring (not shown). The spur roller is rotatably
supported by a spur roller holder 22. The printing medium P is
conveyed in the direction of arrow B, being clipped by two pairs of
rollers, i.e., a roller pair consisting of the conveying roller 14
and the pinch roller 15, and a roller pair consisting of the
discharging roller 20 and the spur roller. However, the printing
medium is clipped and conveyed only by either roller pair while
printing is performed on a front or rear edge of the printing
medium in the "margin-less printing".
[0041] With the arrangement described above, intermittent
repetition of main printing scanning by the printing head cartridge
3 and a given amount of conveying operation allows an image to be
formed one after another on the printing medium P.
[0042] In a position (for example, a position corresponding to a
home position) outside a printing scanning area of the carriage 2,
a recovery device to make the printing head recover from a
discharge failure is disposed. The recovery device includes a
capping mechanism 11 to cap the discharge port surface of the
printing head, and a wiping mechanism 12 and a suction member 10 to
clean the discharge port surface of the printing head. With the
discharge port surface capped with the capping mechanism 11, the
suction member 10 forcibly discharges the ink from the discharge
port, and thereby viscosity-increased ink, bubbles or the like
existing within an ink flow channel in the nozzle can be removed.
Also, when no printing operation is performed, the discharge port
surface of the printing head is capped with the capping mechanism
11, and thereby the printing head can be protected and the ink can
be prevented from evaporating from the discharge port and from
drying.
[0043] On the other hand, the wiping mechanism 12 is arranged in
the vicinity of the capping mechanism 11 to serve to wipe an ink
droplet or the like off the discharge port surface of the printing
head. The recovery device comprising the capping mechanism 11, the
wiping mechanism 12, and the suction member 10 enables the ink
discharge condition of the printing head to be normally
maintained.
<Control Architecture of the Ink Jet Printing Apparatus>
[0044] FIG. 3 is a block diagram showing a control configuration of
the printing apparatus applied in the present embodiment. Referring
to the figure, there is shown a controller 600 which governs
control of the entire printing apparatus. The controller 600 is
provided with an MPU 601, a ROM 602, an ASIC 603, a RAM 604, a
system bus 605, an A/D converter 606, and the like.
[0045] The ROM 602 stores programs corresponding to a control
sequence to be executed by the MPU 601, required tables, other
fixed data, and the like. The ASIC 603 serves to generate control
signals to control the carriage motor M1, the conveyor motor M2,
and a printing head 31. The RAM 604 is utilized as an area for
decompression of image data or as a working area for program
execution. The system bus 605 interconnects the MPU 601, the ASIC
603, and the RAM 604 to transmit and receive data among them. And,
the A/D converter 606 inputs and A/D-converts analog signals from a
group of sensors 630 and sends digital signals to the MPU 601.
[0046] A host device 610, being externally connected, is connected
through an interface 611 to the printing apparatus in the present
embodiment. The host device 610 may be of any form if it serves as
a source of supply of image data to the printing apparatus, and a
computer, a reader for image scanning, a digital camera or the like
is applicable. The interface 611 is capable of sending and
receiving a variety of commands and status signals or the like of
the printing apparatus in addition to the image data.
[0047] A group of switches 620 comprises switches to receive
command inputs from an operator, such as a power switch 621, a
printing switch 622 to give a command to start printing, and a
recovery switch 623 to give a direction to initiate a recovery
operation. A group of sensors 630 to detect a status of the
apparatus comprises a position sensor 631 such as a photo-coupler
to detect the home position and a temperature sensor 632 to detect
environmental temperature.
[0048] Further, there are shown a carriage motor driver 640 to
drive the carriage motor Ml and a conveyor motor driver 642 to
drive the conveyor motor M2.
[0049] When a printing command is inputted from the host device
610, the printing apparatus body analyzes the command and
decompresses image data to a decompression buffer in the RAM 604.
The decompressed image data is subjected to a given processing and
then stored in a printing buffer in the RAM 604. For printing
scanning, the ASIC 603 transmits drive data to the printing head 31
while having a direct access to the printing buffer in the RAM
604.
[0050] Next, a printing method used when "margin-less printing" is
performed in the apparatus in the present embodiment will be
described.
[0051] FIGS. 4A and 4B are enlarged views of a platen 400 provided
in the printing apparatus in the present embodiment. FIG. 4A is a
perspective view and FIG. 4B is a cross-sectional view. The platen
400 has upwardly projecting ribs 401 and 402. Thus, the printing
medium P passing across the platen 400 is conveyed in the direction
of B (sub-scanning direction) while being supported by top faces of
the ribs 401 and 402. Disposed between the ribs 401 and 402 is a
groove 404 with an ink absorber 403 therein, which receives ink
that has off the printing medium during "margin-less printing". It
should however be noted that providing the groove 404 with the ink
absorber 403 is not essential for the margin-less printing.
[0052] FIGS. 5A to 5C are schematic views illustrating a positional
relationship between the printing medium P and the printing head 31
in the vicinity of the platen 400 when "margin-less printing" is
performed.
[0053] On starting printing, in order to first perform the printing
on a front edge Pa, the printing medium P is conveyed to a position
where the front edge Pa is disposed between the ribs 401 and 402.
This state is shown in FIG. 5A. When a positioning operation of the
printing medium P is completed, the printing head 31 performs
scanning in a main scanning direction and discharges ink droplets
onto the front edge Pa (refer to FIG. 5B). At this moment, nozzles
that actually perform a discharge operation are a part of the
nozzles arranged in the printing head 31.
[0054] FIG. 6 is a schematic view illustrating an arrangement of
discharge ports of the printing head 31 applied in the present
embodiment and an area of discharge ports that practically perform
a discharge operation when printing is performed on the front and
rear edges in "margin-less printing". As already described in FIG.
1, the printing head 31 in the present embodiment includes the
nozzle array 4OBk for black, nozzle array 40C for cyan, nozzle
array 40M for magenta, and nozzle array 40Y for yellow, and in each
nozzle array, 256 nozzles are arranged at a predetermined pitch in
the sub-scanning direction (direction B).
[0055] When the printing apparatus is in a normal printing mode,
not "margin-less printing" and when, even in the "margin-less
printing" mode, an image is printed in an area other than the front
and rear edges, all of the 256 nozzles of each color are used for
discharging. However, when the printing is performed on the front
or rear edge in the "margin-less printing", only 64 nozzles
included in area A are used to form the image.
[0056] Image data to be printed on the endmost portion of the
printing medium is created, extending off the front edge Pa to the
outside. The purpose of this is to ensure formation of an image
with no margin even if there are slight variations in conveyance
accuracy and discharging direction of the printing apparatus. To
this end, a portion facing area A of the printing head 31 is
preliminarily provided with the absorber 403. Therefore, the ink
discharged running off the endmost portion of the printing medium
can be almost completely received by the absorber 403. The
arrangement like this applies to right and left edges of the
printing medium.
[0057] When one-line printing scanning is completed, the printing
medium P is conveyed by the conveying roller 14 and a next printing
scanning is performed. The next printing scanning is also provided
to a printing for which only the 64 nozzles included in area A are
used. Such main printing scanning and conveying operation are
repeated, and when no ink comes to run off the front edge Pa even
if the discharge is performed by all of the nozzles of the printing
head 31, the range of the nozzles allowed to perform the discharge
on the printing head 31 is expanded to the whole area. Thereafter,
the printing scanning by all of the 256 nozzles and the conveying
operation corresponding to a printing width of this printing
scanning are repeated until printing in the vicinity of the rear
edge Pb of the printing medium P.
[0058] FIG. 5C shows a state in which printing is performed in the
vicinity of the rear edge Pb. Also in this state, the 64 nozzles
included in area A are used to discharge the ink, running off the
rear edge Pb to the outside. As is the case with the front edge,
the ink discharged running off is almost completely received by the
absorber 403.
[0059] As in the present embodiment, any arrangement in which the
printing medium P is moved while being supported by the top faces
of the ribs 401 and 402 formed in a position projecting beyond the
absorber 403 and the platen plane prevents the printing medium P
from making contact with the absorber 403 and the back side thereof
from being contaminated.
<Preliminary Discharge Operation>
[0060] Hereinafter, a preliminary discharge sequence during
printing in the present embodiment will be described.
[0061] FIG. 7 is a flow chart illustrating a preliminary discharge
control processing. This processing is carried out by the MPU 601
reading and executing a control program stored in the ROM 602.
[0062] While the printing apparatus is waiting for printing data,
i.e., no printing operation is being performed, the discharge port
surface of the printing head 31 is capped in the home position.
When reception of a printing command from the host device 610 is
confirmed, the MPU 601 operates the capping mechanism 11 to open
the discharge port surface of the printing head 31 (step S301). And
in a subsequent step S302, a preliminary discharge from all of the
nozzles toward the capping mechanism 11 is performed.
[0063] Next, in step S303, a printable time (PENBL) is initialized
to a predetermined value. The printable time (PENBL) is defined as
a time for which the printing head is expected to normally perform
a subsequent discharge even in a state where the discharge is not
being performed. An initial value of PENBL is determined in
accordance with performance of the printing head and the printing
apparatus.
[0064] In step S304, a measured value (Dcount(i); i=1 to N, where N
is a total number of nozzles) of a nozzle counter which measures
the number of discharge actuations for each nozzle of the printing
head 31 is initialized to "0".
[0065] The process then goes to step S305 to start an interrupt
timer to create timing for updating the printable time (PENBL) at
predetermined time intervals. In the present embodiment, an
interrupt time interval (TINRT) is 50 msec. Interrupt processing in
the present embodiment will be briefly described below.
[0066] FIG. 8 is a flow chart illustrating the interrupt processing
by the interrupt timer. First, in step S801, a judgment is made
whether or not a next printing scanning is to be provided to the
front or rear edge in the "margin-less printing". A method of the
judgment may be a known one. For example, when printing is
performed on the front or rear edge in the "margin-less printing",
a predetermined memory within the printing apparatus is set to "1";
otherwise it is set to "0". And the memory value is referenced for
judgment. If, in step S801, it is judged that the next printing
scanning is not provided to the front or rear edge in the
"margin-less printing", the process goes to step S805.
[0067] In step S805, a check is made to see if measured values
(Dcount(i)=1, N) of nozzle counters of all the nozzles for all the
colors reach a predetermined threshold value (TH). In the present
embodiment, TH is set to 3. If all of the measured values of the
nozzle counters satisfy Dcount.gtoreq.3, the process goes to step
S807 to reset the printable time (PENBL) for initialization. On the
other hand, if the measured value of any one of the nozzle counters
satisfies Dcount<3, the process goes to step S806 to subtract 50
msec from the printable time (PENBL) to update the printable time
(PENBL).
[0068] If, in step S801, it is judged that the next printing
scanning is provided to the front or rear edge in the "margin-less
printing", the process goes to step S802. In step S802, a check is
made to see if the measured values (Dcount(i)=1, N) of 64 nozzle
counters included in area A for all the colors reach the threshold
value (TH). That is, if all of the measured values of the nozzle
counters included in area A satisfy Dcount.gtoreq.3, the process
goes to step S803 to reset the printable time (PENBL) for
initialization. If the measured value of any one of the nozzle
counters satisfies Dcount<3, the process goes to step S804 to
subtract 50 msec from the printable time (PENBL) to update the
printable time (PENBL).
[0069] When setting of the printable time (PENBL) is completed by
steps S803 to S807, the process goes to step S808 to initialize all
of the measured values (Dcount(i); i=1 to N) of the nozzle counters
to "0". This is the end of the interrupt processing.
[0070] The interrupt processing described in FIG. 8, if the timer
is already started by step S305 in FIG. 7, is executed every 50
msec even during processing of a subsequent step S306 and following
steps.
[0071] Now, going back again to the flow chart of FIG. 7, when a
printing operation is started in step S306, the printing head 31 is
moved to perform printing scanning in step S307. The printing
apparatus in the present embodiment performs so-called
bidirectional printing, in which printing is performed by
discharging ink in both forward and backward scanning directions of
the carriage. Thus, in each printing scanning, the carriage is
first accelerated to a predetermined speed and ink is discharged on
the printing medium during movement at a constant speed of the
predetermined speed. And then, the carriage is decelerated and the
direction of the movement is reversed. This process is carried out
as one printing scanning.
[0072] In the present embodiment, however, processing of step S308
is simultaneously performed immediately before the carriage 2 is
decelerated. In step S308, a judgment is made whether or not all
printing tasks within a page are completed in current printing
scanning. If it is judged that they are completed, this processing
will be terminated. If it is judged that image data to be printed
still exits, the process goes to step S309.
[0073] In step S309, a current printable time (PENBL) is compared
with a time (Tscan) required for a next printing scanning. If PENBL
is equal to or greater than Tscan, the next printing scanning is
deemed to be possible without any preliminary discharge operation
and the process returns to step S307. On the other hand, if PENBL
is smaller than Tscan, a preliminary discharge operation is judged
to be necessary before the next printing scanning and the process
goes to step S310.
[0074] In step S310, the preliminary discharge operation of the
printing head 31 is performed. In the present embodiment, a
preliminary discharge position is a capping position as the home
position. The preliminary discharge may be performed on all the
nozzles for all the colors, but if the next printing scanning is
provided to the front or rear edge in the "margin-less printing",
the preliminary discharge may be performed on only the nozzles
included in area A.
[0075] In a subsequent step S311, the printable time (PENBL) is
reset to the initial value.
[0076] Further, in step S312, all of the measured values
(Dcount(i); i=1 to N) of the nozzle counters are reset to "0".
Thereafter, the process returns to step S307 for the next printing
scanning.
[0077] Incidentally, even after this processing has been completed
as a result of the judgment in step S308, if a next printing
command is inputted in a relatively short time, the process can be
started with step S307. However, if no printing command is inputted
in a predetermined time, the printing head 31 is moved to the home
position and capped by the capping mechanism 11.
[0078] As described above, according to the present embodiment,
even when the time (Tscan) required for a next printing scanning is
compared with the printable time (PENBL) for which printing is
possible without any preliminary discharge with each completion of
printing scanning in accordance with the conventional preliminary
discharge method, nozzles in an area where discharge is not
performed in the next printing scanning are excluded from judgment
on the printable time (PENBL). That is, even in such a situation
where printing is being performed on the front or rear edge in the
"margin-less printing", there is no chance that the preliminary
discharge is improperly performed for nozzles not used for the
printing. Consequently, the decrease in the throughput and the
amount of ink consumption associated with the preliminary discharge
can be minimized.
SECOND EMBODIMENT
[0079] In the above-mentioned embodiment, a printing mode,
"margin-less printing" has been described, but the present
invention is not applicable only to the printing mode, "margin-less
printing". It is broadly applicable to a printing mode in which
printing scanning is performed using only a part of a plurality of
nozzles provided in the printing head. Hereinafter, application to
a normal printing mode, not "margin-less printing" will be
described.
[0080] As described above, the printing medium is conveyed by two
pairs of rollers. One of the two pairs of rollers is a pair of
rollers located upstream of the printing head, specifically, a pair
of rollers consisting of the conveying roller 14 and the pinch
roller 15. The other is a pair of rollers located downstream of the
printing head, specifically, a pair of rollers consisting of the
discharging roller 20 and the spur roller.
[0081] When printing is performed on a central part, not the front
and rear portions of the printing medium, the printing medium is
retained and conveyed by these two pairs of rollers. Therefore, the
conveyance accuracy of the printing medium is high. When printing
is performed on the front and rear portions of the printing medium,
however, the printing medium is retained and conveyed by only one
of these two pairs of rollers. Hence, the conveyance accuracy of
the printing medium is low.
[0082] In this case, as described in the Japanese Patent
Application Laid-open No. 2002-137371, when printing is performed
on the front and rear portions of the printing medium, it is useful
to reduce the number of nozzles used and the amount of each
conveyance, compared to when the printing is performed on the
central part. According to this approach, the printing medium can
be conveyed with a relatively high accuracy at the front and rear
portions.
[0083] Incidentally, in accordance with the above-mentioned
approach, even in the normal printing mode, not the "margin-less
printing", when printing is performed on the front and rear
portions, the range of use of the nozzles is limited, compared to
when the printing is performed on the central part. Then, as with
the "margin-less printing" in the first embodiment, when printing
is performed on the front and rear portions, only the nozzles in
the limited range of use (area of use) are used as objects of
judgment on the printable time (PENBL). Specifically, as described
in FIG. 7 and FIG. 8, the current printable time (PENBL) is
compared with the time (Tscan) required for a next printing
scanning only for nozzles to be used. And, if PENBL is equal to or
greater than Tscan, it is judged that the next printing scanning
can be performed without any preliminary discharge operation, and
the next printing scanning is performed without any preliminary
discharge operation. On the other hand, if PENBL is smaller than
Tscan, it is judged that the preliminary discharge operation is
necessary before the next printing scanning is performed, and the
preliminary discharge is performed before the next printing
scanning.
[0084] According to the foregoing arrangement, even in the normal
printing mode, not the "margin-less printing", the nozzles in the
area (range) where the discharge is not performed in the next
printing scanning can be excluded from judgment on the printable
time (PENBL). Accordingly, an improper preliminary discharge can be
prevented.
OTHER EMBODIMENTS
[0085] In addition, the foregoing first and second embodiments are
arranged to compare the printable time (PENBL) with the time
required for the next printing scanning (Tscan), but the present
invention is not limited thereto. For a printing apparatus capable
of setting the initial value of PENBL to a greater value in
advance, another unit, for example, a plurality of printing
scanning units may be set up and both may be compared to perform
the preliminary discharge.
[0086] Further, in the foregoing description, the flow chart (FIG.
7) based on the preliminary discharge sequence described in the
Japanese Patent Application Laid-open No. 2004-082629, is used, but
the present invention is not limited to such process. Instead of
adjusting the printable time (PENBL) at the predetermined timing as
in the above-mentioned Publication, for example, the arrangement as
described in the Japanese Patent Application Laid-open No.
63-252748 is also acceptable. If any printing apparatus has a
device for counting the number of discharges on a nozzle-by-nozzle
basis and also includes a mechanism for determining whether or not
the preliminary discharge is performed by the use of the count
value, the present invention can effectively function.
[0087] Furthermore, in the foregoing first and second embodiments,
descriptions have been made using the arrangement wherein the
preliminary discharge operation is performed toward the capping
mechanism 11 in the home position, but the present invention is not
limited thereto. Among recent ink jet printing apparatuses, there
are many types of printing apparatus that have a preliminary
discharge pad for receiving the preliminary discharge pre-mounted
in a closer position than the capping mechanism 11 on both sides of
the printing area in the carriage scanning direction. With such
arrangement, even when the preliminary discharge is needed during
printing operation, the carriage 2 does not have to be moved to the
capping mechanism 11 every time. Since the preliminary discharge
operation can be performed on the preliminary discharge pad located
in a closer position, it is possible to perform the preliminary
discharge operation more efficiently in terms of the
throughput.
[0088] Besides, in the foregoing first and second embodiments,
there has been described a form in which the range of the nozzles
to be used is limited for the front-portion or rear-portion
printing in the "margin-less printing" or "normal printing", but
the present invention is not limited to this form. Any ink jet
printing apparatus that has a mechanism capable of preliminarily
detecting that printing scanning is performed by nozzles included
in a part of the nozzle area provided in the printing head can
achieve the advantageous effect of the present invention. That is,
as shown in the flow chart of FIG. 8, providing a process and
device for judging whether or not a next printing operation is to
be performed only by a predetermined part of the nozzles avoids
decreasing the throughput and consuming more ink than necessary
because of the preliminary discharge operation.
[0089] Moreover, in the foregoing embodiments, the ink jet printing
apparatus arranged to discharge the ink from the nozzles by the use
of thermal energy has been described as an example, but the present
invention is not limited thereto. A printing apparatus arranged to
discharge ink from nozzles by the use of mechanical vibrations of
piezo elements or the like is, of course, applicable. Thus, any ink
jet printing apparatus that printings an image by the use of the
printing head provided with a plurality of nozzles capable of
discharging ink can completely achieve the advantageous effect of
the present invention.
[0090] The present invention has been described in detail with
respect to preferred embodiments, and it will now be apparent from
the foregoing to those skilled in the art that changes and
modifications may be made without departing from the invention in
its broader aspect, and it is the intention, therefore, in the
appended claims to cover all such changes and modifications as fall
within the true spirit of the invention.
[0091] This application claims priority from Japanese Patent
Application No. 2005-198953 filed Jul. 7, 2005, which is hereby
incorporated by reference herein.
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